Field-of-View Distortion Calibration and Compensation for Ultra-high Accuracy Video-Based Metrology Systems

摘要

Field-of-View (FOV) distortion affects measurement accuracy by generating location-dependent results in video-based metrology systems. For ultra-high accuracy systems equipped with high-quality lenses, this error can be as small as the uncertainty of obtainable dimensional references. In this research, we develop a method that calibrates the distortion using an uncertified planar artifact. Since the measurement is performed on a plane with a (nominal) constant magnification, we can decouple the calibration for distortion and the calibration for pixel scaling factors, eliminating the need for high-accuracy dimensional references. We first establish a distortion model, and then we solve the model parameters by nonlinear least squares fitting. Furthermore, we find the significant distortion terms by adding them one by one to the model and comparing the fitting residual and convergence. Experimental results of the method on five system configurations show reduced measurement variation across the FOV by up to 80%.